In recent years, many studies have shown that the quality of male semen has a downward trend year by year, leading to an increasing proportion of male factors with reproductive disorders [1] [2] [3]. The internal factors causing the decline of male semen quality mainly include genetic factors, anatomical and physiological factors, and the external factors include environmental factors, lifestyle factors, mental factors and so on [4] [5]. Studies have shown that climate factors and air pollution may affect male reproductive ability. Many studies are committed to the impact of exposure to environmental chemicals and poisons on male reproductive health, like smoking, occupational Lead (Pb), traffic pollution such as nitrogen oxides, sulfur compounds, and sulfur oxides [6] [7] [8] [9]. In the past 100 years, the global average temperature has risen by 0.74˚C, and the average temperature in China has risen by 0.79˚C. In the past 30 years, industry in China has developed rapidly, which results in increasing environmental pollution, especially the air and water pollution caused by energy utilization and industrial production [10].

Various researchers demonstrate that changes in temperature and photoperiod are partly responsible for the periodic changes in sperm parameters [11]. Significant geographic differences in sperm concentration have been reported in Europe, North America, Asia, and Africa [4] [12]. Human and animal studies have shown that male semen quality including quantity, vitality, and fertility has a statistical difference from season to season [13] [14] [15] [16].

Clinically, the semen traits and parameters of the same patient are apparently different in various testing periods, including the total sperm count, sperm concentration, total motility, progressive motility (PR) and so on. This study aims to explore the differences of male semen parameters in different seasons of a year, so as to explore the potential influencing factors of spermatogenesis and male reproductive ability.

The aim of this study was to investigate the relationship between sperm parameters and environmental factors.

* p > 0.05 in spring and autumn; ** p > 0.05 in spring and summer; *** p > 0.05 in autumn and winter.

* p > 0.05.

Previous studies have shown that sperm concentrations have been declining in recent decades, with the average human sperm concentration dropping by about 50 percent over the past 50 years, from 113 × 10⁶/ml to 61 × 10⁶/ml [12]. This trend is similar to our study. The average semen concentration was 42.34 ± 28.50 × 10⁶/ml. The semen concentration declined from 43.74 ± 29.97 per ml in the year of 2018 to 41.32 ± 26.44 per ml in the year of 2020, which was much lower than previous studies. Although sperm concentration decreased, semen volume and the proportion of PR increased, resulting in an increase in the total number of PR. Total number of sperm decreased, but there was no significant statistical significance. There were other factors in and out of the body that affecting male fertility, so no firm conclusions can be drawn from semen analysis alone. According to the records of the national meteorological station obtained from Guangzhou Climate Center, the annual average temperature, air pressure and air humidity in Guangzhou had no significant variations from 2018 to 2020. Therefore, the trend of decreasing or increasing among parameters may also be related to other factors, such as environmental pollution, mental stress, and extracellular environment of spermatogenesis [20]. But the timespan is only three years, more data are needed.

In our study, there was a strong positive correlation between sperm motility and PR (r = 0.934, p = 0.000). Total sperm number was positively correlated with sperm concentration and total PR (r = 0.826, p = 0.000; r = 0.857, p = 0.000). There was a strong correlation between semen concentration and total PR number (r = 0.755, p = 0.000), which indicate that semen concentration and total sperm number may better reflect semen quality than other parameters. In the evaluation of male pregnancy rate, semen concentration and total sperm number can be highly concerned parameters in clinic.

The climate factor itself varies with the season, with both temperature and humidity triggering physiological responses that regulate body temperature. In recent years, several studies have addressed the possible relationship between rising temperatures and the ability of human reproduce [21] [22]. Other factors of climate, such as atmospheric pressure and exposure to sunlight, may also affect sperm quality [23]. The latter affects reproduction directly through endocrine regulation, but also indirectly by influencing solar radiation [16]. All of these factors should be considered when discussing the overall impact of climate on sperm quality.

Guangdong has a subtropical monsoon climate，spring is warm and rainy, summer is hot and humid, winter is mild and dry, the four seasons are relatively distinct [18] [19]. Our study found that there were seasonal differences in sperm quality, and the sperm quality was relatively high in winter and spring, which was consistent with the study of Levitas et al. who assessed 6455 semen samples and found that the sperm quantity and quality were higher in winter and spring [24]. Seasonal changes in chromatin condensation in human sperm seem to confirm this hypothesis [25]. Studies in Italy have also shown that semen changes may follow a seasonal pattern, but it needs at least two years of data to support [26]. Our study collected semen analysis data for three years, with more than 20,000 samples, which can reflect the relationship between sample parameters and seasons.

Although the data support the view that sperm parameters change seasonally in normal and oligospermic sperm samples, no relationship was found between the seasonal patterns of sperm parameters and human pregnancy [13]. Therefore, although there were better sperm parameters in both spring and winter, further research is needed to determine whether higher treatment success rates will be achieved for infertile patients during these seasons.

In humans, the effect of seasonal rotation on sperm parameters is still controversial, and some studies have not formalized the effect of season on sperm parameters [27]. It has been suggested that sperm quality parameters are more likely to be related to climatic factors measured two months before semen collection, rather than in the same month [13]. Therefore, we moved the weather data forward 72 days and matched it with the semen analysis data. We speculated that climate factors played a certain role in the spermatogenesis and sperm development, although it did not provide enough information statistically. However, the influence of temperature, humidity and air pressure on sperm parameters was still objective (p < 0.01). The higher the temperature, the higher the humidity, the poorer the sperm quality. Therefore, in the clinical analysis of semen results, it is necessary to consider the factors of current season and comprehensively evaluate the semen results.

In terms of insolation duration, animal model studies suggested that seasonal variations may be mediated by endogenous mechanisms related to daylight length [28]. Our data showed that insolation duration had no significant effect on any of the parameters of semen analysis, which is similar to the results of a study in Turkey [29]. It is possible that the effects of sunlight on the change of human semen parameters may be relatively slow, which requires long-term observation and comparison, such as decades or even hundreds of years, or the data of regions with different insolation duration.

Our study indicates that semen quality might affected by season and related to temperature, humidity and atmospheric pressure suggesting that in addition to the use food supplement and medication [30], changes in these three factors may improve semen quality, and fertility guidance may also vary by season. Studies have determined that any factor that may increase testicular temperature, such as cryptorchidism, outdoor high-temperature operations, and saunas will have an adverse impact on spermatogenesis [31] [32]. It is recommended that the patient may take appropriate measures to reduce testicular temperature to improve sperm quality such as avoiding study and work in overheated environment, wearing boxer shorts [33]. There are few studies on the effects of humidity and pressure around testis on sperm quality, but together with temperature, they are a group of inseparable indicators, best testicular environmental indicators might be found in following studies.

Unfortunately, the semen analysis data in February 2020 were lacked due to COVID-19. In addition, we only discussed the results of routine semen analysis. Post-testicular factors also play a significant role in sperm fertilization, including the ability to acquire motility, recognize and bind zona pellucida, and fuse with oocytes. These different properties are acquired gradually and simultaneously as sperm pass through the epididymis. Therefore, sperm morphology, membrane function and spermatoplasm environment may also be affected by the external environment, which together play an important role in spermatogenesis maturation.

Finally, seasonal factors should be considered when evaluating male reproductive ability. Except for considering conventional semen analysis parameters, other factors should also be comprehensively analyzed, and adjust the treatment and intervention measures to improve semen quality and fertility according to the actual situation of the environment.

The authors declare no conflicts of interest regarding the publication of this paper.

Zhang, Y.N., Huang, S.Z. and Wang, X.W. (2021) Sperm Quality and Environment: A Retrospective, Cohort Study among 21,715 Semen Samples in a Southern Province of China. Advances in Sexual Medicine, 11, 73-85. https://doi.org/ 10.4236/asm.2021.114005